1. Technical Field
The present invention relates to magnetic ferrite used in a multilayer ferrite chip component such as a multilayer ferrite chip bead and a multilayer inductor and used in an integrated multilayer component represented by an Lc integrated multilayer component, and to a multilayer ferrite chip component.
2. Background Art
A multilayer ferrite chip component and an integrated multilayer component (collectively referred to as a xe2x80x9cmultilayer ferrite chip componentxe2x80x9d in the specification) are used in various electric appliances because of a small volume and high reliability. The multilayer ferrite chip component is normally manufactured by the following process. A sheet or paste for a magnetic layer made of magnetic ferrite and paste for an internal electrode are made into a monolithic laminated strucure using a thick film stacking technology, and then sintered. Then, paste for an external electrode is printed or transferred on a surface of the sintered body obtained, and then baked. Note that sintering after obtaining the monolithic laminated strucure is referred to as co-firing. Ag or an Ag alloy is used as a material for the internal electrode because of their low resistivity. Accordingly, as for the magnetic ferrite material constituting the magnetic layer, it is an absolute condition that the material is capable of co-firing, in other words, capable of being sintered at a temperature lower than the melting point of Ag or an Ag alloy. Therefore, whether or not the magnetic ferrite can be sintered at a temperature lower than the melting point of Ag or an Ag alloy is a key to obtaining a multilayer ferrite chip component of high density and high-level characteristics.
NiCuZn ferrite is known as the magnetic ferrite that can be sintered at a temperature lower than the melting point of Ag or an Ag alloy. at a temperature lower than the melting point of Ag or an Ag alloy. Specifically, the NiCuZn ferrite using raw material powder with a specific surface area of about 6 m2/g or greater produced by fine milling can be sintered at a temperature lower than the melting point of Ag (961.93xc2x0 C.). Accordingly, the NiCuZn ferrite is widely used in the multilayer ferrite chip components.
In recent years, hexagonal ferrite has drawn attention with an increase of a clock frequency. There are six kinds of the hexagonal ferrite, namely, an M type, a U type, a W type, an X type, a Y type and a Z type, which have characteristics different from cubic ferrite of an Mn based ferrite and an Ni based ferrite. Among these kinds, the Z type has a general formula of M3Me2Fe24O41. Here, M denotes alkaline-earth metal, and Me denotes bivalent metal ions. Among the Z types of the hexagonal ferrite, a Z type hexagonal ferrite containing cobalt metal ions has large anisotropy. Thus, the Z type hexagonal ferrite containing cobalt metallic ions is capable of having high permeability up to a frequency range higher than that of spinel ferrite. The Z type hexagonal ferrite containing cobalt metallic ions is referred to as Co2Z.
Although the fact that the Z type hexagonal ferrite has an excellent high frequency characteristic has been known from before, it has not been put into practical use yet due to several problems. Specifically, phases of M, W and Y appear in the course of generation of Z phase, and generation of the different phases reduces the permeability. Moreover, it is also pointed out that sintered hexagonal ferrite of the Z type has low sintered body density. If the sintered body density is low, low mechanical strength of the sintered body when used as a surface mount component becomes a problem. In addition, the sintered body density and the permeability are closely related to each other, as the permeability itself is reduced if the sintered body density is low. Thus, original magnetic properties cannot be exerted.
Japanese Patent Laid-Open No. Hei9 (1997)-110432 gazette discloses a hexagonal ferrite material in which sintered body density thereof is increased and the permeability reduction in high frequency region is suppressed. The hexagonal ferrite material disclosed in Japanese Patent Laid-Open No. Hei9 (1997)-110432 gazette is characterized in that SiO2 and CaO are added by predetermined amounts. However, the hexagonal ferrite material disclosed in Japanese Patent Laid-Open No. Hei9 (1997)-110432 gazette is based on the assumption that the material is sintered at a temperature in a range from 1150xc2x0 C. to 1350xc2x0 C. Accordingly, the co-firing cannot be performed, and application to the multilayer ferrite chip components is difficult.
Japanese Patent Laid-Open No. Hei9 (1997)-167703 gazette discloses an approach to a low-temperature sintering of a hexagonal ferrite material. Specifically, the gazette points out that a composition of (Ba, Sr, Pb)3(Co1-xCux)2Fe24O41, that is, substitution of a portion of the alkaline-earth metal with Pb and also substitution of a portion of Co with Cu, allows the hexagonal ferrite material to be dense at a low temperature. However, the hexagonal ferrite material obtained by Japanese Patent Laid-Open No. Hei9 (1997)-167703 gazette has the phases of M, Y, W, X and U as main phases, and has not obtained the hexagonal ferrite material having the Z phase as a main phase, which is highly permeable to the high frequency range.
As described above, a hexagonal ferrite material capable of sintering at a low temperature and having the Z phase as a main phase has not been obtained yet.
An object of the present invention is to provide a hexagonal ferrite material that can be applied to a multilayer ferrite chip component because of capability of low-temperature sintering and that has Z phase as a main phase, and a multilayer ferrite chip component using such material.
Conventionally, hexagonal ferrite of the Z type usable in a GHz-range has not been able to sinter at a temperature lower than the melting point of Ag, which constitutes a material for an internal electrode. This is because magnetic properties cannot be obtained unless the ferrite is sintered at a high temperature in a range from 1250xc2x0 C. to 1350xc2x0 C. Therefore, it has not been possible to obtain a multilayer ferrite chip component which requires co-firing with Ag by using the hexagonal ferrite of the Z type. Although a hexagonal ferrite material that can be sintered at a low temperature has been proposed, such material does not have Z phase as a main phase. The inventors therefore examined a calcining temperature, a grain size distribution of powder before sintering, a powder specific surface area, and an additive to a main composition, and solved the foregoing problems.
The present invention provides magnetic ferrite powder in which a peak intensity ratio of the Z phase of the hexagonal ferrite (M3Me2Fe24O41: M=one or more kinds of alkaline-earth metal, Me=one or more kinds selected from Co, Ni, Mn, Zn, Mg and Cu) is 30% or higher in X-ray diffraction and a peak value of grain size distribution is within a range from 0.1 xcexcm to 3 xcexcm.
The magnetic ferrite powder of the present invention can be added with one or more kinds selected from borosilicate glass, zinc borosilicate glass, Bi2O3 based glass, CuO and Bi2O3, by 0.5 wt % to 20 wt %. Among the above, it is preferable to add CuO and Bi2O3 by 0.5 wt % to 20 wt % in total, or to add Bi2O3 based glass and CuO by 1 wt % to 20 wt % in total. In particular, it is preferable to add Bi2O3 based glass by 3 wt % to 7 wt % and CuO by 3 wt % to 7 wt %.
The present invention also provides magnetic ferrite powder in which Z phase (M=Ba, Me=one or more kinds selected from Co, Ni, Mn, Zn, Mg and Cu) indicated as M3Me2Fe24O41 forms a main phase and a powder specific surface area is 5 m2/g to 30 m2/g. In the magnetic ferrite powder of the present invention, the magnetic ferrite having an excellent high frequency characteristic can be obtained by substituting a portion of Ba with Sr, and calcining is enabled at a temperature lower than a conventional calcining temperature.
The present invention further provides a sintered body of magnetic ferrite in which Z phase (M=Ba, Me=one or more kinds selected from Co, Ni, Mn, Zn, Mg and Cu) indicated as M3Me2Fe24O41 forms a main phase, CuO and Bi2O3 are included by 0.5 wt % to 20 wt % in total, CuO mainly exists in grains, and Bi2O3 mainly exists in grain boundaries. In this sintered body, CuO and Bi2O3 effectively function to sintering at a temperature lower than 960xc2x0 C. In addition, in the sintered body of magnetic ferrite of the present invention, a portion of Ba can be substituted with Sr.
Moreover, the present invention provides a sintered body of magnetic ferrite in which Z phase (M=Ba, Me=one or more kinds selected from Co, Ni, Mn, Zn, Mg and Cu) indicated as M3Me2Fe24O41 forms a main phase, and Bi2O3 based glass and CuO are added by 1 wt % to 20 wt % in total.
Furthermore, the present invention provides a multilayer ferrite chip component in which a magnetic ferrite layer and an internal electrode are stacked alternately, and which comprises an external electrode electrically connected with the internal electrode. The magnetic ferrite layer has the Z phase of the hexagonal ferrite (M3Me2Fe24O41: M=one or more kinds of alkaline-earth metal, Me=one or more kinds selected from Co, Ni, Mn, Zn, Mg and Cu) as a main phase in X-ray diffraction, and is constituted of a sintered body of magnetic ferrite having a mean grain size of 1 to 5 xcexcm. The internal electrode is constituted of Ag or an Ag alloy.
The multilayer ferrite chip component of the present invention is the one in which the magnetic ferrite layer and the internal electrode layer are co-fired, and density of the magnetic ferrite layer can be made to be 5 g/cm3 or higher. Moreover, in the multilayer ferrite chip component of the present invention, it is preferable that the magnetic ferrite layer includes CuO and Bi2O3 by 0.5 wt % to 20 wt % in total, CuO mainly exists within grains, and Bi2O3 mainly exists within grain boundaries. In addition, in the multilayer ferrite chip component of the present invention, it is preferable that the magnetic ferrite layer includes Bi2O3 based glass and CuO by 1 wt % to 20 wt % in total.
The multilayer ferrite chip component of the present invention described above can be obtained by a manufacturing method of the multilayer ferrite chip component of the present invention as follows. Specifically, it is a manufacturing method of a multilayer ferrite chip component in which a magnetic ferrite layer and an internal electrode are stacked with each other. The method comprises the steps of mixing raw material powder of magnetic ferrite; calcining the mixed raw material powder in a temperature range of 1200xc2x0 C. or higher; milling an obtained calcined body so as to make a peak value of the grain size distribution fall into a range from 0.1 xcexcm to 3 xcexcm; obtaining a sheet or paste for forming a magnetic layer by using obtained milled powder; obtaining a laminated green body by alternately stacking the sheet or the paste and a material for the internal electrode; and sintering the laminated green body at a temperature lower than 960xc2x0 C. Here, the magnetic ferrite layer consists of a sintered body of magnetic ferrite having Z phase (M3Me2Fe24O41: M=one or more kinds of alkaline-earth metal, Me=one or more kinds selected from Co, Ni, Mn, Zn, Mg and Cu) of hexagonal ferrite as a main phase in X-ray diffraction. In the manufacturing method of the present invention, it is preferable that a powder specific surface area of each raw material powder is 4.5 m2/g or greater, and a powder specific surface area of the milled powder is in a range from 8 to 20 m2/g.